Such a tunnel lining is known from Ausrian Patent Specification 389,149. A tunnel lining of that kind affords the basic advantage that prefabricated parts can be used, which can be assembled to form modular tubbing rings, which are held together by plugs so that the blocks can be installed immediately after the excavation, and, if possible, under the protection of the shield tail of tunnel-driving machine. A deviation of the course of the tunnel lining from a straight line can be achieved by the use of tubbing blocks, which can be assembled to form tubbing rings having end faces which extend in planes including an acute angle with each other in such a position that two rings, which are assembled to be equal and opposite to each other, constitute a cylindrical tubular section having parallel end faces and the rings can be rotated from that position to permit a deviation of the course of the lining toward the sides and toward the top and bottom. In the design which is known from Austrian Patent Specification 389,149 the keys substantially constitute sliding guides of the blocks as they are assembled and the blocks abut each other almost without a gap at their oblique side faces. In Austrian Patent Application A 323/92, which is no prior publication, it has been proposed to provide keys which are compressible and made, e.g., of properly deformable material, or as tubular members, so that they keep the blocks spaced apart so as to define a gap and under the rock pressure can be compressed so as to reduce the width of the gaps. In that case it is possible to use identical blocks for yieldable and non-yieldable linings.
In soils and rocks which have only a poor inherent carrying capacity or a high deformation capacity, tunnel linings having a limited radial yieldability may be used to permit the economical provision of a lining made of prefabricated parts and to use only elements which can be made at low cost. Because the lining is radially deformable, the pressure exerted by the soil and/or rock initially deforms to a predetermined extent the lining against the deformation resistance which is defined by the upsettable elements. If the extent of the deformation which is possible in view of the properties of the soil and/or rock is sufficiently large the pressure exerted by the soil and/or rock may be caused to decrease as the deformation proceeds and/or the rock may come to a standstill when the defined deformation has been effected. In that case the lining will be subjected to a lighter load than a rigid lining. Examples of additional possible uses of a tunnel or shaft lining of the present kind are shafts and tunnels having thick overburdens and/or subjected to strong rock pressures in Alpine transit routes.
It is also known to provide tunnel linings having relatively large gaps. According to French Patent Specification 2,627,802, housings for containing upsettable elements are provided between tubbings which in their basic shape are rectangular or corrugated or made of corrugated steel material and are joined to the abutting longitudinal edges of the tubbings by screws, optionally with interposed gaskets. In other known designs, rodlike upsettable elements are accommodated in the gaps and are supported at the edges of the two lining elements which define the gap or the upsettable elements may be accommodated in part in said edges. In another known design one element has an edge which faces the gap and carries supporting plates for supporting plugs, which constitute deformable members, which can slidably be inserted into tubes, which extend from the edge of the other element and are installed in the element and at the end of the tube are provided with clamping members or cutting members for acting on the plugs so that the insertion of the plugs into the tubes is opposed by an exactly defined resistance. From Published German Application 21 01 092 it is known to provide yieldable inserts of wood or chipboard between adjacent tubbings. Soviet Union Patent Specification 823,500 teaches the use of concrete tubbings, which have straight parallel longitudinal edges formed with recesses, such as V-shaped grooves, which are used to support upsettable metal bodies, and gaps which are not required as upsettable zones may subsequently be filled with concrete. With the exception of the design disclosed in the above-mentioned French patent specification the entire lining of the tunnel is rendered unstable in part by the existing gaps. The field of application of said known designs is also restricted by the fact that the upsettable elements are mounted at the edges that are parallel to the longitudinal axis of the tunnel. Besides, if upsettable zones are provided only in certain regions, larger gaps will be required for the accommodation of the upsettable elements so that different dimensions will result in the overall lining and tubbings having larger peripheral dimensions must be used in regions having no upsettable zones.